The hypothesis that quiescent CD4+ T lymphocytes carrying proviral DNA provide a reservoir for human immunodeficiency virus-type 1 (HIV-1) in patients on highly active antiretroviral therapy (HAART) was examined. In a study of 22 patients successfully treated with HAART for up to 30 months, replication-competent virus was routinely recovered from resting CD4+ T lymphocytes. The frequency of resting CD4+ T cells harboring latent HIV-1 was low, 0.2 to 16.4 per 10(6) cells, and, in cross-sectional analysis, did not decrease with increasing time on therapy. The recovered viruses generally did not show mutations associated with resistance to the relevant antiretroviral drugs. This reservoir of nonevolving latent virus in resting CD4+ T cells should be considered in deciding whether to terminate treatment in patients who respond to HAART.

https://science.sciencemag.org/content/sci/278/5341/1295.full.pdf

Identification of a Reservoir for HIV-1 in Patients on Highly Active Antiretroviral Therapy

In evaluating current combination drug regimens for treatment of human immunodeficiency virus (HIV) disease, it is important to determine the existence of viral reservoirs. After depletion of CD8 cells from the peripheral blood mononuclear cells (PBMCs) of both patients and normal donors, activation of patient CD4 lymphocytes with immobilized antibodies to CD3 and CD28 enabled the isolation of virus from PBMCs of six patients despite the suppression of their plasma HIV RNA to fewer than 50 copies per milliliter for up to 2 years. Partial sequencing of HIV pol revealed no new drug resistance mutations or discernible evolution, providing evidence for viral latency rather than drug failure.

https://science.sciencemag.org/content/sci/278/5341/1291.full.pdf

Recovery of replication-competent HIV despite prolonged suppression of plasma viremia.

Combination therapy for HIV-1 infection can reduce plasma virus to undetectable levels, indicating that prolonged treatment might eradicate the infection. However, HIV-1 can persist in a latent form in resting CD4+ T cells. We measured the decay rate of this latent reservoir in 34 treated adults whose plasma virus levels were undetectable. The mean half-life of the latent reservoir was very long (43.9 months). If the latent reservoir consists of only 1 x 10(5) cells, eradication could take as long as 60 years. Thus, latent infection of resting CD4+ T cells provides a mechanism for lifelong persistence of HIV-1, even in patients on effective anti-retroviral therapy.

Latent infection of CD4 + T cells provides a mechanism for lifelong persistence of HIV-1, even in patients on effective combination therapy

Although highly active antiretroviral therapy (HAART) in the form of triple combinations of drugs including protease inhibitors can reduce the plasma viral load of some HIV-1-infected individuals to undetectable levels, it is unclear what the effects of these regimens are on latently infected CD4+ T cells and what role these cells play in the persistence of HIV-1 infection in individuals receiving such treatment. The present study demonstrates that highly purified CD4+ T cells from 13 of 13 patients receiving HAART with an average treatment time of 10 months and with undetectable (<500 copies HIV RNA/ml) plasma viremia by a commonly used bDNA assay carried integrated proviral DNA and were capable of producing infectious virus upon cellular activation in vitro. Phenotypic analysis of HIV-1 produced by activation of latently infected CD4+ T cells revealed the presence in some patients of syncytium-inducing virus. In addition, the presence of unintegrated HIV-1 DNA in infected resting CD4+ T cells from patients receiving HAART, even those with undetectable plasma viremia, suggests persistent active virus replication in vivo.

https://www.pnas.org/content/pnas/94/24/13193.full.pdf

Presence of an inducible HIV-1 latent reservoir during highly active antiretroviral therapy

Analysis of changes in viral load after initiation of treatment with potent antiretroviral agents has provided substantial insight into the dynamics of human immunodeficiency virus type 1 (HIV-1). The concentration of HIV-1 in plasma drops by approximately 99% in the first two weeks of treatment owing to the rapid elimination of free virus with a half-life (t1/2) of < or =6 hours and loss of productively infected cells with a t1/2 of 1.6 days. Here we show that with combination therapy this initial decrease is followed by a slower second-phase decay of plasma viraemia. Detailed mathematical analysis shows that the loss of long-lived infected cells (t1/2 of 1-4 weeks) is a major contributor to the second phase, whereas the activation of latently infected lymphocytes (t1/2 of 0.5-2 weeks) is only a minor source. Based on these decay characteristics, we estimate that 2.3-3.1 years of a completely inhibitory treatment would be required to eliminate HIV-1 from these compartments. To eradicate HIV-1 completely, even longer treatment may be needed because of the possible existence of undetected viral compartments or sanctuary sites.

Decay characteristics of HIV-1-infected compartments during combination therapy

The capacity of HIV-1 to establish latent infection of CD4+ T cells may allow viral persistence despite immune responses and antiretroviral therapy. Measurements of infectious virus and viral RNA in plasma and of infectious virus, viral DNA and viral messenger RNA species in infected cells all suggest that HIV-1 replication continues throughout the course of infection. Uncertainty remains over what fraction of CD4+ T cells are infected and whether there are latent reservoirs for the virus. We show here that during the asymptomatic phase of infection there is an extremely low total body load of latently infected resting CD4+ T cells with replication-competent integrated provirus (<10(7) cells). The most prevalent form of HIV-1 DNA in resting and activated CD4+ T cells is a full-length, linear, unintegrated form that is not replication competent. The infection progresses even though at any given time in the lymphoid tissues integrated HIV-1 DNA is present in only a minute fraction of the susceptible populations, including resting and activated CD4+ T cells and macrophages.

Yen Hong Kuo

Papers

Quantification of latent tissue reservoirs and total body viral load in HIV-1 infection